Each of the roughly 100,000 genes encoded in the human genome is subject to individual dosage control. The systems that regulate gene expression respond to a wide variety of developmental and environmental stimuli, thus allowing each cell type to express a unique and characteristic subset of its genes, and to adjust the dosage of particular gene products as needed. The importance of dosage control is underscored by the fact that targeted disruption of key regulatory molecules in mice often results in drastic phenotypic abnormalities [Johnson, R. S., et al., Cell, 71:577-586 (1992)], just as inherited or acquired defects in the function of genetic regulatory mechanisms contribute broadly to human disease.
The regulatory mechanisms controlling the transcription of protein- coding genes by RNA polymerase II have been extensively studied. RNA polymerase II and its host of associated proteins are recruited to the core promoter through non-covalent contacts with sequence-specific DNA binding proteins [Tjian, R. and Maniatis, T., Cell, 77:5-8 (1994); Stringer, K. F., Nature (London), 345:783-786 (1990)]. An especially prevalent and important subset of such proteins, known as transactivators, typically bind DNA at sites outside the core promoter and activate transcription through space contacts with components of the transcriptional machinery, including chromatin remodeling proteins [Tjian, R. and Maniatis, T., Cell, 77:5-8 (1994); Stringer, K. F., Nature (London), 345:783-786 (1990); Bannister, A. J. and Kouzarides, T., Nature, 384:641-643 (1996); Mizzen, C. A., et al., Cell, 87:1261-1270 (1996)]. The DNA-binding and activation functions of transactivators generally reside on separate domains whose operation is portable to heterologous fusion proteins [Sadowski, I., et al., Nature, 335:563-564 (1988)]. Though it is believed that activation domains are physically associated with a DNA-binding domain to attain proper function, the linkage between the two need not be covalent [Belshaw, P. J., et al., Proc. Natl. Acad. Sci. USA, 93:4604-4607 (1996); Ho, S. H., et al., Nature (London), 382:822-826 (1996)]. In many instances, the activation domain does not appear to contact the transcriptional machinery directly, but rather through the intermediacy of adapter proteins known as coactivators [Silverman, N., et al., Proc. Natl. Acad. Sci. USA, 91:11005-11008 ((1994); Arany, Z., et al., Nature (London), 374:81-84 (1995)].
The importance of controlled gene expression in human disease and the information available to date relating to the mechanisms of gene regulation have fueled efforts aimed at discovering means of overriding endogenous regulatory controls or of creating new signaling circuitry in cells [Belshaw, P. J., et al., Proc. Natl. Acad. Sci. USA, 93:4604-4607 (1996); Ho, S. H., et al., Nature (London), 382:822-826 (1996); Rivera, V. M., et al., Nat. Med., 2:1028-1032; Spencer, D. M., et al., Science, 262:1019-1024 (1993)]. Of particular interest in this regard are small, membrane-permeant molecules designed to modulate gene transcription in living cells [Belshaw, P. J., et al., Proc. Natl. Acad. Sci. USA, 93:4604-4607 (1996); Ho, S. H., et al., Nature (London), 382:822-826 (1996); Rivera, V. M., et al., Nat. Med., 2:1028-1032; Spencer, D. M., et al., Science, 262:1019-1024 (1993)]. All such efforts involved genetic engineering of transcriptional modulatory protein domains such as naturally-occurring VP16. The present invention takes a significant departure from such art by relying upon chemical rather than biological means to harness the transcriptional machinery.